In automated assembly lines for producing optical fiber connectors, it is often necessary to find a feature or segment along the periphery of the connector, and particularly, along the fiber or ferrule of the connector. The reason is that sometimes the connector or parts thereof need to be rotated in a proper posture for examination or for engaging another part with the connector. An example of such a requisite procedure involves placement of a coupling grip onto a connector.
A coupling grip is a device that is placed around the end tip of a connector to permit engagement of the connector with a coupling. In the case of a conventional SC optical fiber connector, the coupling grip is a square-shaped sleeve that is slid over the square-shaped periphery of the end tip of the connector and mounted thereto. In order for the square-shaped sleeve to be slid over the square-shaped end tip, the square-shaped coupling grip must be physically oriented in the proper posture with respect to the square-shaped end tip.
One known technique that can be used for determining the orientation of the coupling grip involves pattern matching. In the pattern matching technique, a stored bit pattern of the segment of interest, or the target segment, is compared with a segment in the image, or the test segment. They are compared on a pixel-by-pixel basis, and an error is derived based upon the difference in pixel intensities. The error is then compared to a threshold. If the error falls within a predefined threshold, then a match is concluded. Otherwise, when the error falls outside of the threshold, it is concluded that a match has not occurred, and another segment of the test image is analyzed. Because the very heart of the pattern matching technique uses pixel-based digitization, this technique is very sensitive to noise. Also, in environments where the likelihood of two samples being alike is slim, as in the case of a coupling grip, matches are problematic. Finally, the pattern matching technique is extremely time consuming and impractical for a fully automated assembly line.
Another known technique that could be adapted to determine the orientation of a coupling grip involves the use of a mathematical model known as a Hough transform. Use of a Hough transform is described in U.S. Pat. No. 5,179,419 to Palmquist et al., as an example. The Hough transform is generally a technique for filtering data in an image by defining appropriate data thresholds. This technique could be adapted in order to determine the orientation of an edge of the coupling grip.
Although this technique yields accurate results, it is very computationally intensive, requires an inordinate amount of time, thereby making it impractical for a fully automated connector assembly line, and is limited to first degree polynomial fits, which would make it impractical for discovering segments exhibiting complex patterns, i.e., multiple directions.